Several methods and approaches for fault location in high voltage power systems have been developed and employed. One approach has been to use voltage/current transducers located at terminals, between which the power lines to be monitored run. Inductive current transformers are used to provide a measurement of instantaneous current in a transmission line.
However, inductive current transformers (CTs) may become saturated under transmission line faults with high fault current, which often takes place during faults close to CTs installation point. The saturation is possible especially for faults in which there is a slowly decaying dc component in the fault current.
Saturation of CTs influences operation of protective relays as well as the accuracy of fault location for inspection-repair purposes. Note that accuracy of both one-end and two-end fault locators can be adversely affected by the saturated CTs. U.S. Pat. No. 4,559,491 which is titled Method and device for locating a fault point on a three-phase power transmission line, discloses a method and device wherein a single end fault locator uses measurements of voltages and currents from a particular side [1], and, if at the side where the fault locator is installed the CTs are saturated, the achieved accuracy of fault location could be unsatisfactory.
Better conditions may be obtained for the above single end fault location for the case when the CTs are saturated at the terminal which is opposite to the fault locator installation point. In such cases the input post fault currents of the fault locator are not contaminated due to saturation of CTs. However, greater accuracy of fault location in such cases can be achieved if impedance of a source from the remote side (where CTs are saturated) is known. The remote source impedance cannot be determined with one-end measurements and therefore in some applications the one-end fault locator may be augmented by inputting a value for the remote end impedance. This value may be measured by the other remote device and sent via a communication channel. Note that in this case the measured remote source impedance can differ greatly from the actual value due to saturation of CTs. Using an inaccurately measured source impedance could deteriorate substantially the fault location accuracy.
Similarly, accuracy of fault location with two-end methods, as for example with the representative methods disclosed in U.S. Pat. No. 5,455,776 which is titled Automatic fault location system, and in U.S. Pat. No. 6,256,592B1 [2–3] which is titled Multi-ended fault location system, are also affected by saturation of CTs. The method of U.S. Pat. No. 5,455,776 [2] uses symmetrical components of voltages and currents from both sides of a line. In case of the method disclosed in U.S. Pat. No. 6,256,592B1 [3] the amplitude of the remote current and the amplitude of the remote source impedance, both determined for the negative sequence, are utilized for calculating a distance to fault. The distortion of the currents, resulting from any saturated CTs, affects the accuracy of both the above two-end fault location techniques [2–3]. No countermeasures against the possible effects of saturation are disclosed in the cited methods [2–3].